DEAR DR. BLONZ: Usually, when I eat leafy green salads in restaurants, I have no adverse physical reaction. But a few times, I have eaten this type of salad in restaurants and it caused me severe diarrhea, which strikes within a half-hour after leaving the restaurant. I am usually homebound by this for the next 24 hours, feeling weak and lethargic. This does not happen when I eat other foods, or homemade green salad. Can you tell me what chemical the restaurant or food processing companies may be adding? And how can I protect myself from this happening again? -- H.K.

DEAR H.K.: In addition to the lousy way it makes us feel, it is always a disappointment when eating -- an activity meant to provide nourishment and satisfaction -- makes us ill. And it can be troublesome to attempt to figure out what might have been responsible. The list of possibilities might include a developing illness, a reaction to one or more medications, a food allergy or sensitivity, or an eating establishment’s sanitation issue.

Food poisoning is on the “suspect” list in the case you describe, especially given that you have not experienced this type of reaction when eating other foods or making salads at home. There is the possibility that something contaminated was included in the meal; this can include the food, salad dressing, condiments, beverage, dishes, silverware or any unclean item or surface you were exposed to while visiting the establishment. (I have assumed your hands were washed.)

It is difficult to identify the responsible element(s) until some theme emerges. Thoughts that added “chemicals” are responsible would not be at the top of my list, unless such events occur regularly. As for greens: Last year, there were several incidences of E. coli infections linked to romaine lettuce.

Is a particular restaurant more involved than others with these episodes? You may be able to get more information by speaking with friends who frequent that same establishment. Or, you could check social media to see if others have had similar experiences -- but I advise caution, as critical posts can be baseless comments made by competitors.

Bottom line: With the details provided, it is difficult to point your fork at the salad greens and say they made you sick. With no obvious answer at this time, a shift to “detective mode” will increase the odds for success. That said, I hope that this does not happen again! Write back if you learn more. For more on food safety, see b.link/food22.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: During a recent online nutrition class, there was a discussion about whether fruits and berries have the most antioxidants, and other beneficial substances, when they are the sweetest. This was the position taken by the teacher and supported by some students, but I argued the opposite. Who is correct? -- P.E., Chicago

DEAR P.E.: You have my support. The “mission” in the plant world, if we can think of it like that, is to grow and reproduce to propagate the species. Unlike animals, plants can’t get up and run away from dangers. Successful plants have evolved to resist threats from limited resources, insects, microorganisms and animals, to name a few. The environment is also a player. A report in the February 2020 issue of the National Academy of Sciences’ journal reported that unchecked global warming might contribute to the extinction of up to one-third of all plant species by 2070.

Successful plants have evolved to create physical and chemical protections to facilitate their growth and the development of seeds needed for reproduction. Chemicals produced by plants (phytochemicals) represent an in-house tool kit for defense and repairs.

Where do antioxidants fit in the picture? From the moment its first shoot emerges, a plant relies on the sun for energy. Too much radiation from the sun, however, can result in oxidative damage to plant tissues. Fruits and vegetables make antioxidants as protection against destructive oxidation. These antioxidants are for the plant’s protection, not ours.

Another side of the story involves seed distribution. The wind can serve that purpose; in those instances, seeds are light in weight and designed for flight. Some seeds get distributed through barbs, which get them carried away on animal fur. Other seeds develop inside fleshy fruit that gets consumed by animals, passes through the digestive system and is then deposited in a new location.

Of relevance to your class discussion is that the protective phytochemicals are at their peak before the seed is ripe. The plant’s entire resource investment is near its conclusion. The last thing the plant needs is an animal feeding on the fruit before the seed is ready for the dance. Unripe fruits don’t taste great -- that’s the way it should be -- and antioxidants contribute via their bitter, astringent or acidic tastes.

Once the seed is ripe, however, the goal shifts to facilitating seed distribution. Sweetness develops when “unsweet” complex carbohydrates get broken into simple sugars -- usually fructose, which is about 1.4 times as sweet as sucrose. Along with that come changes in color and odor: all signals to animals that dinner is served.

You can see, and hopefully explain to the class, that a piece of fruit harvested before it reaches its peak ripeness can, of course, be less sweet. But less sweetness doesn’t necessarily mean smaller amounts of beneficial substances.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Is there still vitamin C left after a potato is baked or french-fried? According to a USDA database, one cup of baked potatoes contains about 10 milligrams of vitamin C. Authorities I checked with say that heat destroys vitamin C, and baking or frying exposes potatoes to significant amounts of heat. Are “heated” potatoes still a good source of vitamin C? -- F.D., Anderson, South Carolina

DEAR F.D.: Food preparation methods involving high heat can indeed destroy heat-sensitive (or “heat-labile”) nutrients, which include vitamin C and thiamin (vitamin B1). With normal cooking, this will be a reduction, not an elimination. That level in the USDA database does reflect an estimated 50% reduction of the amount of vitamin C found in a raw potato.

A food is considered to be a “good source” of a nutrient if one serving provides between 10 and 19% of the Daily Value. The adult Daily Value for vitamin C is 60 milligrams. Three-and-a-half ounces (100 grams) of baked potatoes does provide about 10 milligrams of vitamin C, which meets that requirement. There is less vitamin C in french fries, as that process involves higher temperatures (albeit for shorter periods). But even if french fries manage to clear the 10% bar for one or more of the potato’s nutrients, this would not qualify fries as a go-to food to meet your nutritional needs.

DEAR DR. BLONZ: A company that sells Tupelo honey is claiming that it is OK for diabetics because of the levulose content. I am not familiar with levulose. Are you aware of research to affirm that claim? -- G.G., San Jose, California

DEAR G.G.: Sugars can go by multiple names. Fructose, also known as “fruit sugar,” is also called levulose. Glucose can also be called dextrose, or “blood sugar.” Table sugar is made up of glucose bound to fructose, whereas honey also contains these two sugars, but not bound together.

Honey tends to have more fructose than glucose, and Tupelo honey usually has more fructose than other varieties. Does this make it safer for diabetics? Doubtful. There is no magic (or science) to support that claim.

Adjustments can be made to allow for a small amount of honey, when used as a minor ingredient. Still, simple sugars such as honey -- whether Tupelo or clover -- can impact a diabetic’s blood sugar level, so caution is advised. If you have specific questions about your particular situation, it would be beneficial to consult with a registered dietitian.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.